Keep in mind that failed matches don't reset the value of the match variables -- if you later do a regex match you'll want to be sure your $1 isn't from this current match. Example:

$foo = "bungling";
$foo =~ /(ngl.)/; ## $1 is now "ngli"
$matched = $1;     ## $matched = "ngli"
$foo =~ /bung(ngl.)/;  ##  No match!
$matched2 = $1;  ## $matched 2 is now "ngli"
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Also, a lot of programmers will apply regexes against the "default" variable

$_="tricky";  ## usually not assigned explicitly, typically comes in d
+uring a for loop
/tr(.{3})y/;
print $1;    # $1 = "ick"
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